Methods and systems for mobile wimax three-way downlink concurrent processing and three-way handover

ABSTRACT

Methods and apparatus for establishing multiple connections between a wireless device and multiple base stations and transferring data using these connections via different segments of an orthogonal frequency division multiple access (OFDMA) frame are provided. The multiple connections may be used for multi-way (e.g., three-way) concurrent processing, multi-way (e.g., three-way) handover, or a hybrid between concurrent processing and multi-way handover in an effort to increase data throughput for the wireless device.

The present Application for Patent is a Continuation of patentapplication Ser. No. 12/123,411 entitled “METHODS AND SYSTEMS FOR MOBILEWIMAX THREE-WAY DOWNLINK CONCURRENT PROCESSING AND THREE-WAY HANDOVER”filed May 19, 2008, now issued as U.S. Pat. No. 8,223,622, and assignedto the assignee hereof and hereby expressly incorporated by referenceherein.

TECHNICAL FIELD

Certain embodiments of the present disclosure generally relate towireless communication and, more particularly, to establishing multipleconnections between a wireless device and multiple base stations andexchanging data using these connections via different segments of anorthogonal frequency division multiple access (OFDMA) frame.

BACKGROUND

Orthogonal frequency-division multiplexing (OFDM) and OFDMA wirelesscommunication systems under IEEE 802.16 use a network of base stationsto communicate with wireless devices (i.e., mobile stations) registeredfor services in the systems based on the orthogonality of frequencies ofmultiple subcarriers and can be implemented to achieve a number oftechnical advantages for wideband wireless communications, such asresistance to multipath fading and interference. Each base station (BS)emits and receives radio frequency (RF) signals that convey data to andfrom the mobile stations. Typically, a mobile station (MS) onlycommunicates with one base station (e.g., the serving base station) at atime. This BS allocates bandwidth to the MS based on the base station'sown scheduling algorithm, and the MS is restricted from using bandwidthfrom other base stations.

SUMMARY

Certain embodiments of the present disclosure generally relate toestablishing multiple connections between a wireless device and multiplebase stations and exchanging data using these connections via differentsegments of an orthogonal frequency division multiple access (OFDMA)frame. The multiple connections may be used for multi-way (e.g.,three-way) concurrent processing, multi-way (e.g., three-way) handover,or a hybrid between concurrent processing and multi-way handover.

Certain embodiments of the present disclosure provide a method. Themethod generally includes establishing a first connection with a firstbase station, wherein the first connection involves the transfer of datausing a first signal based on a first segment of an OFDMA frame;establishing a second connection with a second base station, wherein thesecond connection involves the transfer of data using a second signalbased on a second segment of the OFDMA frame; and exchanging data withthe first and second base stations via the first and second connectionswithin a time period bounded by the OFDMA frame.

Certain embodiments of the present disclosure provide a receiver forwireless communication. The receiver generally includes firstconnection-establishing logic configured to establish a first connectionwith a first base station, wherein the first connection involves thetransfer of data using a first signal received by the receiver and basedon a first segment of an OFDMA frame; second connection-establishinglogic configured to establishing a second connection with a second basestation, wherein the second connection involves the transfer of datausing a second signal received by the receiver and based on a secondsegment of the OFDMA frame; and data logic configured to exchange datawith the first and second base stations via the first and secondconnections within a time period bounded by the OFDMA frame.

Certain embodiments of the present disclosure provide an apparatus forwireless communication. The apparatus generally includes means forestablishing a first connection with a first base station, wherein thefirst connection involves the transfer of data using a first signalbased on a first segment of an OFDMA frame; means for establishing asecond connection with a second base station, wherein the secondconnection involves the transfer of data using a second signal based ona second segment of the OFDMA frame; and means for exchanging data withthe first and second base stations via the first and second connectionswithin a time period bounded by the OFDMA frame.

Certain embodiments of the present disclosure provide a mobile device.The mobile device generally includes first connection-establishing logicconfigured to establish a first connection with a first base station,wherein the first connection involves the transfer of data using a firstsignal based on a first segment of an OFDMA frame; secondconnection-establishing logic configured to establishing a secondconnection with a second base station, wherein the second connectioninvolves the transfer of data using a second signal based on a secondsegment of the OFDMA frame; and a receiver front end for receiving thefirst and second signals from the first and second base stations via thefirst and second connections within a time period bounded by the OFDMAframe.

Certain embodiments of the present disclosure provide acomputer-readable medium containing a program for wirelesscommunication, which, when executed by a processor, performs certainoperations. The operations generally include establishing a firstconnection with a first base station, wherein the first connectioninvolves the transfer of data using a first signal based on a firstsegment of an OFDMA frame; establishing a second connection with asecond base station, wherein the second connection involves the transferof data using a second signal based on a second segment of the OFDMAframe; and exchanging data with the first and second base stations viathe first and second connections within a time period bounded by theOFDMA frame.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to embodiments, someof which are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalembodiments of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective embodiments.

FIG. 1 illustrates an example wireless communication system, inaccordance with certain embodiments of the present disclosure.

FIG. 2 illustrates various components that may be utilized in a wirelessdevice in accordance with certain embodiments of the present disclosure.

FIG. 3 illustrates an example transmitter and an example receiver thatmay be used within a wireless communication system that utilizesorthogonal frequency-division multiplexing and orthogonal frequencydivision multiple access (OFDM/OFDMA) technology in accordance withcertain embodiments of the present disclosure.

FIG. 4 illustrates an example OFDMA frame for Time-Division Duplex (TDD)with three segments, in accordance with certain embodiments of thepresent disclosure.

FIG. 5 illustrates three connections with different data between awireless device and three base stations for three-way concurrentprocessing, in accordance with certain embodiments of the presentdisclosure.

FIG. 6 is a flow chart of example operations for establishing andexchanging data using multiple connections between a wireless device andmultiple base stations via segments of an OFDMA frame, in accordancewith certain embodiments of the present disclosure.

FIG. 6A is a block diagram of means corresponding to the exampleoperations for establishing and using multiple connections of FIG. 6, inaccordance with certain embodiments of the present disclosure.

FIG. 7 illustrates an example scenario for three-way concurrentprocessing, three-way handover, or a hybrid scheme between them, inaccordance with certain embodiments of the present disclosure.

FIG. 8 illustrates a receiver block diagram configured to time alignsegments of an OFDMA frame received from three different base stations,in accordance with certain embodiments of the present disclosure.

FIGS. 9A-B illustrate scenarios for deleting existing connections andadding new connections as a wireless device changes locations from astarting location in FIG. 7, in accordance with certain embodiments ofthe present disclosure.

FIGS. 10A and 10B illustrate flow charts of example operations foradding new connections and deleting existing connections based onstrength of signals received at a wireless device, in accordance withcertain embodiments of the present disclosure.

FIG. 11 illustrates three connections with different data between awireless device and three base stations for three-way handover, inaccordance with certain embodiments of the present disclosure.

FIG. 12 is a chart comparing and listing the advantages of three-wayconcurrent processing, three-way handover, and a hybrid between them, inaccordance with certain embodiments of the present disclosure.

DETAILED DESCRIPTION

Certain embodiments of the present disclosure provide techniques andapparatus for establishing multiple connections between a wirelessdevice and multiple base stations and exchanging data using theseconnections via different segments of an orthogonal frequency divisionmultiple access (OFDMA) frame. The multiple connections may be used formulti-way (e.g., three-way) concurrent processing, multi-way (e.g.,three-way) handover, or a hybrid between concurrent processing andmulti-way handover in an effort to increase data throughput for thewireless device.

Exemplary Wireless Communication System

The methods and apparatus of the present disclosure may be utilized in abroadband wireless communication system. The term “broadband wireless”refers to technology that provides wireless, voice, Internet, and/ordata network access over a given area.

WiMAX, which stands for the Worldwide Interoperability for MicrowaveAccess, is a standards-based broadband wireless technology that provideshigh-throughput broadband connections over long distances. There are twomain applications of WiMAX today: fixed WiMAX and mobile WiMAX. FixedWiMAX applications are point-to-multipoint, enabling broadband access tohomes and businesses, for example. Mobile WiMAX offers the full mobilityof cellular networks at broadband speeds.

Mobile WiMAX is based on OFDM (orthogonal frequency-divisionmultiplexing) and OFDMA (orthogonal frequency division multiple access)technology. OFDM is a digital multi-carrier modulation technique thathas recently found wide adoption in a variety of high-data-ratecommunication systems. With OFDM, a transmit bit stream is divided intomultiple lower-rate substreams. Each substream is modulated with one ofmultiple orthogonal subcarriers and sent over one of a plurality ofparallel subchannels. OFDMA is a multiple access technique in whichusers are assigned subcarriers in different time slots. OFDMA is aflexible multiple-access technique that can accommodate many users withwidely varying applications, data rates, and quality of servicerequirements.

The rapid growth in wireless internets and communications has led to anincreasing demand for high data rate in the field of wirelesscommunications services. OFDM/OFDMA systems are today regarded as one ofthe most promising research areas and as a key technology for the nextgeneration of wireless communications. This is due to the fact thatOFDM/OFDMA modulation schemes can provide many advantages such asmodulation efficiency, spectrum efficiency, flexibility, and strongmultipath immunity over conventional single carrier modulation schemes.

IEEE 802.16x is an emerging standard organization to define an airinterface for fixed and mobile broadband wireless access (BWA) systems.These standards define at least four different physical layers (PHYs)and one media access control (MAC) layer. The OFDM and OFDMA physicallayer of the four physical layers are the most popular in the fixed andmobile BWA areas respectively.

FIG. 1 illustrates an example of a wireless communication system 100.The wireless communication system 100 may be a broadband wirelesscommunication system. The wireless communication system 100 may providecommunication for a number of cells 102, each of which is serviced by abase station 104. A base station 104 may be a fixed station thatcommunicates with user terminals 106. The base station 104 mayalternatively be referred to as an access point, a Node B, or some otherterminology.

FIG. 1 depicts various user terminals 106 dispersed throughout thesystem 100. The user terminals 106 may be fixed (i.e., stationary) ormobile. The user terminals 106 may alternatively be referred to asremote stations, access terminals, terminals, subscriber units, mobilestations, stations, user equipment, etc. The user terminals 106 may bewireless devices, such as cellular phones, personal digital assistants(PDAs), handheld devices, wireless modems, laptop computers, personalcomputers (PCs), etc.

A variety of algorithms and methods may be used for transmissions in thewireless communication system 100 between the base stations 104 and theuser terminals 106. For example, signals may be sent and receivedbetween the base stations 104 and the user terminals 106 in accordancewith OFDM/OFDMA techniques. If this is the case, the wirelesscommunication system 100 may be referred to as an OFDM/OFDMA system.

A communication link that facilitates transmission from a base station104 to a user terminal 106 may be referred to as a downlink 108, and acommunication link that facilitates transmission from a user terminal106 to a base station 104 may be referred to as an uplink 110.Alternatively, a downlink 108 may be referred to as a forward link or aforward channel, and an uplink 110 may be referred to as a reverse linkor a reverse channel.

A cell 102 may be divided into multiple sectors 112. A sector 112 is aphysical coverage area within a cell 102. Base stations 104 within awireless communication system 100 may utilize antennas that concentratethe flow of power within a particular sector 112 of the cell 102. Suchantennas may be referred to as directional antennas. For example, basestation 104 _(A) may provide directional coverage for sector A 112 _(A),base station 104 _(B) may provide directional coverage for sector B 112_(B), and base station 104 _(C) may provide directional coverage forsector C 112 _(C) as illustrated in FIG. 1.

FIG. 2 illustrates various components that may be utilized in a wirelessdevice 202. The wireless device 202 is an example of a device that maybe configured to implement the various methods described herein. Thewireless device 202 may be a base station 104 or a user terminal 106.

The wireless device 202 may include a processor 204 which controlsoperation of the wireless device 202. The processor 204 may also bereferred to as a central processing unit (CPU). Memory 206, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 204. A portion of thememory 206 may also include non-volatile random access memory (NVRAM).The processor 204 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 206. Theinstructions in the memory 206 may be executable to implement themethods described herein.

The wireless device 202 may also include a housing 208 that may includea transmitter 210 and a receiver 212 to allow transmission and receptionof data between the wireless device 202 and a remote location. Thetransmitter 210 and receiver 212 may be combined into a transceiver 214.An antenna 216 may be attached to the housing 208 and electricallycoupled to the transceiver 214. The wireless device 202 may also include(not shown) multiple transmitters, multiple receivers, multipletransceivers, and/or multiple antennas.

The wireless device 202 may also include a signal detector 218 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 214. The signal detector 218 may detect suchsignals as total energy, pilot energy from pilot subcarriers or signalenergy from the preamble symbol, power spectral density, and othersignals. The wireless device 202 may also include a digital signalprocessor (DSP) 220 for use in processing signals.

The various components of the wireless device 202 may be coupledtogether by a bus system 222, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

FIG. 3 illustrates an example of a transmitter 302 that may be usedwithin a wireless communication system 100 that utilizes OFDM/OFDMA.Portions of the transmitter 302 may be implemented in the transmitter210 of a wireless device 202. The transmitter 302 may be implemented ina base station 104 for transmitting data 306 to a user terminal 106 on adownlink 108. The transmitter 302 may also be implemented in a userterminal 106 for transmitting data 306 to a base station 104 on anuplink 110.

Data 306 to be transmitted is shown being provided as input to aserial-to-parallel (S/P) converter 308. The S/P converter 308 may splitthe transmission data into N parallel data streams 310.

The N parallel data streams 310 may then be provided as input to amapper 312. The mapper 312 may map the N parallel data streams 310 ontoN constellation points. The mapping may be done using some modulationconstellation, such as binary phase-shift keying (BPSK), quadraturephase-shift keying (QPSK), 8 phase-shift keying (8PSK), quadratureamplitude modulation (QAM), etc. Thus, the mapper 312 may output Nparallel symbol streams 316, each symbol stream 316 corresponding to oneof the N orthogonal subcarriers of the inverse fast Fourier transform(IFFT) 320. These N parallel symbol streams 316 are represented in thefrequency domain and may be converted into N parallel time domain samplestreams 318 by an IFFT component 320.

A brief note about terminology will now be provided. N parallelmodulations in the frequency domain are equal to N modulation symbols inthe frequency domain, which are equal to N mapping and N-point IFFT inthe frequency domain, which is equal to one (useful) OFDM symbol in thetime domain, which is equal to N samples in the time domain. One OFDMsymbol in the time domain, N_(s), is equal to N_(cp) (the number ofguard samples per OFDM symbol)+N (the number of useful samples per OFDMsymbol).

The N parallel time domain sample streams 318 may be converted into anOFDM/OFDMA symbol stream 322 by a parallel-to-serial (P/S) converter324. A guard insertion component 326 may insert a guard interval betweensuccessive OFDM/OFDMA symbols in the OFDM/OFDMA symbol stream 322. Theoutput of the guard insertion component 326 may then be upconverted to adesired transmit frequency band by a radio frequency (RF) front end 328.An antenna 330 may then transmit the resulting signal 332.

FIG. 3 also illustrates an example of a receiver 304 that may be usedwithin a wireless communication system 100 that utilizes OFDM/OFDMA.Portions of the receiver 304 may be implemented in the receiver 212 of awireless device 202. The receiver 304 may be implemented in a userterminal 106 for receiving data 306 from a base station 104 on adownlink 108. The receiver 304 may also be implemented in a base station104 for receiving data 306 from a user terminal 106 on an uplink 110.

The transmitted signal 332 is shown traveling over a wireless channel334. When a signal 332′ is received by an antenna 330′, the receivedsignal 332′ may be downconverted to a baseband signal by an RF front end328′. A guard removal component 326′ may then remove the guard intervalthat was inserted between OFDM/OFDMA symbols by the guard insertioncomponent 326.

The output of the guard removal component 326′ may be provided to an S/Pconverter 324′. The S/P converter 324′ may divide the OFDM/OFDMA symbolstream 322′ into the N parallel time-domain symbol streams 318′, each ofwhich corresponds to one of the N orthogonal subcarriers. A fast Fouriertransform (FFT) component 320′ may convert the N parallel time-domainsymbol streams 318′ into the frequency domain and output N parallelfrequency-domain symbol streams 316′.

A demapper 312′ may perform the inverse of the symbol mapping operationthat was performed by the mapper 312, thereby outputting N parallel datastreams 310′. A P/S converter 308′ may combine the N parallel datastreams 310′ into a single data stream 306′. Ideally, this data stream306′ corresponds to the data 306 that was provided as input to thetransmitter 302.

Exemplary OFDMA Frame

Referring now to FIG. 4, an OFDMA frame 400 for a Time-Division Duplex(TDD) implementation is depicted as a typical, but not limiting,example. Other implementations of an OFDMA frame, such as Full andHalf-Duplex Frequency-Division Duplex (FDD) may be used, in which casethe frame is the same except that both downlink (DL) and uplink (UL)messages are transmitted simultaneously over different carriers. In theTDD implementation, each frame may be divided into a DL subframe 402 anda UL subframe 404, which may be separated by a small guard interval—or,more specifically, by Transmit/Receive and Receive/Transmit TransitionGaps (TTG 406 and RTG 407, respectively)—in an effort to prevent DL andUL transmission collisions. The DL-to-UL-subframe ratio may be variedfrom 3:1 to 1:1 to support different traffic profiles.

Within the OFDMA frame 400, various control information may be included.For example, the first OFDMA symbol of the frame 400 may be a preamble408, which may contain several pilot signals (pilots) used forsynchronization. Fixed pilot sequences inside the preamble 408 may allowthe receiver 304 to estimate frequency and phase errors and tosynchronize to the transmitter 302. Moreover, fixed pilot sequences inthe preamble 408 may be utilized to estimate and equalize wirelesschannels. The preamble 408 may contain BPSK-modulated carriers and istypically one OFDM symbol long. The carriers of the preamble 408 may bepower boosted and are typically a few decibels (dB) (e.g., 9 dB) higherthan the power level in the frequency domain of data portions in theWiMAX signal. The number of preamble carriers used may indicate which ofthe three segments 409 of the zone are used. For example, carriers 0, 3,6, . . . may indicate that segment 0 (409 ₀) is to be used, carriers 1,4, 7, . . . may indicate that segment 1 (409 ₁) is to be used, andcarriers 2, 5, 8, . . . may indicate that segment 2 (409 ₂) is to beused.

A Frame Control Header (FCH) 410 may follow the preamble 408, one FCH410 per segment 409. The FCH 410 may provide frame configurationinformation, such as the usable subchannels, the modulation and codingscheme, and the MAP message length for the current OFDMA frame. A datastructure, such as the downlink Frame Prefix (DLFP), outlining the frameconfiguration information may be mapped to the FCH 410. The DLFP forMobile WiMAX may comprise a used subchannel (SCH) bitmap, a reserved bitset to 0, a repetition coding indication, a coding indication, a MAPmessage length, and four reserved bits set to 0. Before being mapped tothe FCH 410, the 24-bit DLFP may be duplicated to form a 48-bit block,which is the minimal forward error correction (FEC) block size.

Following the FCH 410 in each segment 409, a DL-MAP 414 and a UL-MAP 416may specify subchannel allocation and other control information for theDL and UL subframes 402, 404, respectively. In OFDMA, multiple users maybe allocated data regions within the frame 400, and these allocationsmay be specified in the DL and UL-MAP 414, 416. The MAP messages mayinclude the burst profile for each user, which defines the modulationand coding scheme used in a particular link. Since MAP messages containcritical information that needs to reach all users for that segment 409,the DL and UL-MAP 414, 416 may often be sent over a very reliable link,such as BPSK or QPSK with rate ½ coding and repetition coding.

The DL subframe 402 of the OFDMA frame 400 may include DL bursts ofvarious bit lengths containing the downlink data being communicated.Thus, the DL-MAP 414 may describe the location of the bursts containedin the downlink zones and the number of downlink bursts, as well astheir offsets and lengths in both the time (i.e., symbol) and thefrequency (i.e., subchannel) directions. Altogether, the preamble 408,the FCH 410, and the DL-MAP 414 may carry information that enables thereceiver 304 to correctly demodulate the received signal.

Likewise, the UL subframe 404 may include UL bursts of various bitlengths composed of the uplink data being communicated. Therefore, theUL-MAP 416, transmitted as the first DL burst in the DL subframe 402,may contain information about the location of the UL burst for differentusers. The UL subframe 404 may include additional control information asillustrated in FIG. 4, such as a UL Ranging subchannel 422 allocated forthe mobile station to perform closed-loop time, frequency, and poweradjustments during network entry and periodically afterward, as well asbandwidth requests. The UL subframe 404 may also include a UL ACK (notshown) allocated for the mobile station (MS) to feed back a DL hybridautomatic repeat request acknowledgment (HARQ ACK) and/or a UL CQICH(not shown) allocated for the MS to feed back channel state informationon the Channel Quality Indicator channel (CQICH).

Different “modes” may be used for DL and UL transmission in OFDMA. Anarea in the time domain where a certain mode is used is generallyreferred to as a zone. One type of zone is called a DL-PUSC (downlinkpartial usage of subchannels) zone 424 and may not use all thesubchannels available to it (i.e., a DL-PUSC zone 424 may only useparticular subchannels). The DL-PUSC zone 424 may be divided into atotal of six subchannel groups, which can be assigned to up to threesegments 409. Thus, a segment 409 may contain one to six subchannelgroups (e.g., segment 0 may contain two subchannel groups 0 and 1,segment 1 may contain two subchannel groups 2 and 3, and segment 2 maycontain two subchannel groups 4 and 5 as illustrated in FIG. 4). Anothertype of zone is called a DL-FUSC (downlink full usage of subchannels)zone 426. Unlike DL-PUSC, DL-FUSC does not use any segments, but candistribute all bursts over the complete frequency range.

Typically, a frequency reuse factor (K) of 3 is used in which theDL-PUSC zone 424 may be divided into three segments 409 in the frequencydomain according to subchannels. In this scheme, each segment 409 may becomposed of two subchannel groups as illustrated in FIG. 4 and describedabove. The subcarriers in each subchannel group may not be contiguous.Furthermore, each base station 104 may have N sector antennas (e.g.,N=3) on the same cell site in an effort to transmit in N differentdirections, leading to a frequency reuse pattern of N/K (e.g., equal to3/3). In this manner, the cells 102 may be divided into three sectors112, and each segment 409 of the DL-PUSC zone 424 may be associated withone sector 112.

However, one problem with a frequency reuse factor of three (K=3) isthat the downlink transmission for a particular segment can only use onethird of the total bandwidth (e.g., 5 MHz for WiMAX). Therefore, themaximum throughput of a mobile station may be limited to one third ofthe bandwidth of the total allocated spectrum.

Furthermore, a mobile station may be running various servicesconcurrently. For example, a wireless device user may be surfing theInternet, watching a video stream, and voice communicating at the sametime. If all of these services were to be served by one segment, somelinks to these services may be rejected when the sector is loaded anddoes not have sufficient bandwidth to accommodate all the links.Alternatively, if all of the links were to be established, the date rateof each service may most likely be reduced to meet the capacityconstraint of one single segment.

An Example Method for Three-Way Concurrent Processing

In an effort to increase the throughput per mobile station (MS),different downlink connections may be established using multiplesegments in an OFDMA frame. This may allow the MS to utilize bandwidthfrom different segments (up to the full bandwidth of the allocatedspectrum) and may alleviate the bandwidth demand on any one particularsector.

FIG. 5 illustrates such a concurrent processing scheme, with threeconnections (Connection 0, Connection 1, and Connection 2) withdifferent data between a user terminal 106 and three base stations 104for three-way concurrent processing, according to a frequency reusefactor of 3. The DL data being transmitted may be different data fromthe same service or, as illustrated in FIG. 5, may comprise data fromdifferent services, such as voice data 500, Internet data 502, andstreaming video data 504.

The DL data from each connection may be transmitted to the user terminal106 in a different segment 409 of the DL-PUSC zone 424. For example,data for Connection 0 may be transmitted as one or more DL data burstsin Segment 0, data for Connection 1 may be transmitted as DL data burstsin Segment 1, and data for Connection 2 may be transmitted as DL databursts in Segment 2. In this manner, the user terminal 106 may be ableto establish and maintain all three connections, concurrently receivingdifferent DL data potentially from different services without reducingthe data rate of any service, at least up to the limit of the bandwidthallocated per segment.

FIG. 6 is a flow chart of example operations 600 for establishing andexchanging data using multiple connections between a wireless device andmultiple base stations in a mobile WiMAX system, for example, viasegments of an OFDMA frame. The operations 600 may begin, at 602, byestablishing a first connection with a first base station fortransferring data using a first signal based on a first segment of anOFDMA frame. At 604, a second connection with a second base station maybe established for transferring data using a second signal based on asecond segment of the same OFDMA frame. Data may be transferred from thefirst and second base stations to the wireless device using the firstand second connections at 606. From the operations 600, two-wayconcurrent processing may commence. Three-way concurrentprocessing/traffic transfer may occur at 606 if a third connection witha third base station was established after 604 using a third signalbased on a third segment of the same OFDMA frame for K=3.

For example, FIG. 7 illustrates an example scenario for three-wayconcurrent processing. In FIG. 7, a wireless device 700 located insector B 112 _(B) may receive signals from at least three different basestations 104. A first connection 702 between the base station providingcoverage for sector B 112 _(B) and the wireless device 700 may beestablished. The first connection 702 may use segment 0, for example, ofan OFDMA frame in an effort to transmit DL data of a particular serviceto the wireless device 700. A second connection 704 may be establishedbetween the base station providing coverage for sector A 112 _(A) andthe wireless device 700, and a third connection 706 may be establishedbetween the base station providing coverage for sector C 112 _(C) andthe wireless device 700. The second and third connections 704, 706 mayuse segment 1 and segment 2, for example, of the same OFDMA frame in aneffort to simultaneously transmit different DL data to the wirelessdevice 700.

In order for the receiver 304 of the user terminal 106 to demodulate,decode, and interpret the DL data received from the multipleconnections, the receiver 304 may time align the different segments sothat they may be synchronized to line up with the boundary of the OFDMAframe. This temporal alignment issue may arise because the differentbase stations may not be synchronized (i.e. asynchronous base stationtiming) in some wireless systems and furthermore, because of thedifferent propagation delays from the different base stations 104 to theuser terminal 106.

FIG. 8 illustrates an example receiver block diagram 800 configured totime align the various segments 409 of an OFDMA frame received fromthree different base stations 104. The received signal 802 may havethree different time adjustments applied in the delay blocks 804, eachtime adjustment based on the delay from one of the base stations. Thesegments may be synchronized using the pilots of the preamble 408, forexample, and the delay may be applied in the delay blocks 804accordingly to produce time-aligned signals 806. A fast Fouriertransform (FFT) may be applied to each of the time-aligned signals 806in the FFT blocks 808 to transform these signals from the time-domaininto the frequency-domain.

Once the time-aligned signals 806 have been transformed into thefrequency-domain, the data for certain subchannels may be extractedaccording to the subchannel groups indicated in the DLFP 412 of the FCH410 for a particular segment 409. The extracted data for a particularsegment may be demodulated and decoded in the Demodulator/Decoder blocks810 in order to interpret the downlink data from the three connections.

As a wireless device changes location, signals received from a certainbase station may become too weak to use with acceptable bit error ratio(BER) to achieve a minimum quality of service (QoS) for a particulartype of service, and therefore this connection may be dropped. However,the wireless device may move closer to another base station with astronger signal, and a new connection may be established to replace thedropped connection. For example, the wireless device 700 of FIG. 7 maymove far enough away from the base station 104 ₁ serving sector A 112_(A) such that the second connection 704 is dropped, as illustrated inFIG. 9A. If there is not another base station with a signal strongenough to provide a new connection, the wireless device may operate withtwo-way concurrent processing, having only the first and thirdconnections 702, 706 to transfer data.

Referring now to FIG. 9B, the wireless device 700 may continue movingand enter a new sector A 912 _(A), wherein the new sector A 912 _(A)uses the same subchannel groups as the segment 409 for the previouslydescribed sector A 112 _(A). The signal strength from the sector Bantenna of the second base station 104 ₂ providing coverage for sector B112B may be too weak, and the wireless device 700 may also receive astrong signal from the sector A antenna of the second base station 104 ₂providing coverage for the new sector A 912 _(A). Hence, the firstconnection 702 may be dropped, and a fourth connection 708 may beestablished with the wireless device 700.

Now that the wireless device 700 may be operating with two-wayconcurrent processing and the segment associated with sector B is notbeing used, the wireless device may be able to add a new connection to afourth base station 104 ₄. The fourth base station 104 ₄ may providecoverage for a different sector B 912 _(B), wherein the new sector B 912_(B) uses the same subchannel groups as the segment 409 for thepreviously described sector B 112 _(B). Once the signal from the fourthbase station 104 ₄ as received by the wireless device 700 is strongenough, a fifth connection 710 may be established with the wirelessdevice 700, such that the wireless device again operates with three-wayconcurrent processing to increase its DL data throughput.

As the wireless device 700 continues to move, the device may move farenough away from the third base station 104 ₃ serving sector C 112 _(C)such that the third connection 706 is dropped, as illustrated in FIG.9B. The device may have been or, as it moves closer, may start receivingsignals from a fifth base station 104 ₅, and the device may be able toadd a new connection. The fifth base station 104 ₅ may provide coveragefor a different sector C 912 _(C), wherein the new sector C 912 _(C)uses the same subchannel groups as the segment 409 for the previouslydescribed sector C 112 _(C). Once the signal from the fifth base station104 ₅ as received by the wireless device 700 is strong enough, a sixthconnection 712 may be established with the wireless device 700, suchthat the wireless device again operates with three-way concurrentprocessing to increase its DL data throughput.

FIG. 10A is a flow chart of example operations 1000 for adding newconnections and deleting existing connections based on strength ofsignals received at a wireless device in a mobile WiMAX system, forexample. In this manner, the wireless device may continuously monitorthe signal strength of existing segment(s) being processed and thesignal strength of potential new segments not currently being processed.

The operations 1000 may begin, at 1002, by determining whether thepreamble signal strength from a new segment (i.e., a new sector) asreceived by the wireless device is greater than an add threshold(S_ADD). If so, then at 1004, whether the new segment uses differentsubchannel groups from the existing segments with previously establishedconnections may be determined. Therefore, if the new segment has signalstrength greater than S_ADD and uses different subchannel groups thanexisting segments, a connection using the new segment may be added tothe wireless device. However, if the new segment has a signal strengthless than or equal to S_ADD at 1002 or uses the same subchannel groupsas existing segments at 1004, the connection using the new segment maynot be added.

At 1008, whether any existing segments with established connections havea preamble signal strength less than a drop threshold (S_DROP) may bedetermined If so, then at 1010, established connection(s) using existingsegments with the low signal strength may be dropped at 1010, and theoperations 1000 may repeat starting at 1002. If there are no existingsegments with signal strength less than S_DROP, the operations mayrepeat at 1002.

For some embodiments as illustrated in the operations 1050 of FIG. 10B,if the preamble signal strength of a new segment is greater than S_ADDat 1002, but the new segment uses the same subchannel groups as theexisting segment(s) at 1004, a connection with the new segment may stillbe established. At 1052, whether the signal strength of the new segmentis better by a certain margin than the existing segment using the samesubchannel groups may be determined. If not, the connection using thenew segment may not be added. However, if the signal strength of the newsegment is significantly better (i.e., better than the existing segmentby the margin), than the connection using the existing segment may bereplaced with a new connection using the new segment at 1054 beforedetermining whether any existing segments have a signal strength belowS_DROP at 1008. In this manner, a new connection having a segment with abetter signal strength may be added without having to wait for aconnection using any existing segment with a weak signal strength (e.g.,below S_DROP) to be deleted.

Exemplary Three-Way Handover

Conventionally in mobile WiMAX, a mobile station may communicate onlywith one serving base station at a time. This base station allocatesbandwidth to the mobile station based on the base station's scheduleralgorithm. To switch services from one base station to another (or fromone sector to another), the mobile station typically performs a handover(also known as a handoff) to switch from its serving base station to atarget base station. Also conventionally, the mobile station can onlyuse bandwidth (e.g., certain subchannel groups) from its serving basestation, but cannot use bandwidth from non-serving base stationsproviding coverage in neighboring sectors.

In an effort to increase the data throughput for one segment, accordingto certain embodiments of the present disclosure, different downlinkconnections may be established using multiple segments (e.g., two orthree) in an OFDMA frame, such that each DL connection transmits datathrough only one segment as described above for concurrent processing.However, the mobile station may receive and parse the multiple segmentsat the same time. The multiple segments may contain data from the sameservice such that the mobile station may select the segment (from theconnections with multiple base stations) that offers the mobile stationthe best bandwidth grant and may communicate with the selected segment.The mobile station may change the selection of the best segment on anOFDMA frame-by-frame basis, which may be considered as a multi-wayhandover (e.g., a three-way handover between three different basestation sectors for a frequency reuse factor of three). As such, themobile station may view all of the multiple segments received as comingfrom serving sectors. This scheme of multi-way handover may allow themobile station to increase the data throughput within a segment,although the segment used may be changing.

FIG. 11 illustrates such a handover scheme for increased datathroughput, with three connections (Connection 0, Connection 1, andConnection 2) with different data between a user terminal 106 and threebase stations 104 for three-way handover, according to a frequency reusefactor of 3. The DL data being transmitted may be data from the sameservice, such as voice data 1100 (as shown), Internet data, or streamingvideo data. The DL data from each connection may be transmitted to theuser terminal 106 in a different segment 409 of the DL-PUSC zone 424.For example, data for Connection 0 may be transmitted as one or more DLdata bursts in Segment 0, data for Connection 1 may be transmitted as DLdata bursts in Segment 1, and data for Connection 2 may be transmittedas DL data bursts in Segment 2. In this manner, the user terminal 106may be able to establish and maintain all three connections as describedabove in the operations 600 of FIG. 6, selecting the segment with thebest bandwidth grant for communication. The user terminal 106 may ignorethe other two segments until one of these segments offers the bestbandwidth grant in a subsequent OFDMA frame.

Exemplary Hybrid Handover/Concurrent Processing

For some embodiments, the multi-way concurrent processing and handoverschemes described above may be combined to form a hybrid scheme. As anexample with K=3, three connections may be established with a mobilestation. Two of the connections (e.g., Connection 0 and 1 using segments0 and 1 of an OFDMA frame) may have DL data from the same service withsimilar data, and the third connection (e.g., Connection 2 using segment2) may have DL data from a different service. The mobile station mayselect between segments 0 and 1 depending on which segment offers thebest bandwidth grant (for a two-way handover) and may perform concurrentprocessing with DL data from the selected segment and from segment 2 inan effort to increase the bandwidth usage.

Exemplary Multiple WiMAX Connections

FIG. 12 is a chart 1200 comparing and listing the advantages ofthree-way concurrent processing, three-way handover, and a hybridbetween them as described above. The chart 1200 lists the type 1202,provides a brief description 1204 of each type, and notes an advantage1206 of each type over conventional K=3 schemes where the maximumthroughput of a mobile station may be limited to one third of thebandwidth of the total allocated spectrum (e.g., 5 MHz for WiMAX).

Although embodiments of the present disclosure are described withrespect to establishing two or three connections when considering afrequency reuse factor of 3, the techniques and apparatus describedabove may be expanded to work with other configurations. For example,for cells divided into six sectors, up to six connections may beestablished, and a subchannel group within the OFDMA frame may be usedfor each connection instead of a segment.

The operations described above may be performed by various hardwareand/or software component(s) and/or module(s) corresponding to a numberof means-plus-function blocks. For example, the operations 600 of FIG. 6described above may be performed by various hardware and/or softwarecomponent(s) and/or module(s) corresponding to the means-plus-functionblocks 600A illustrated in FIG. 6A. In other words, blocks 602 through606 illustrated in FIG. 6 correspond to means-plus-function blocks 602Athrough 606A illustrated in FIG. 6A.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals and the like that may be referencedthroughout the above description may be represented by voltages,currents, electromagnetic waves, magnetic fields or particles, opticalfields or particles or any combination thereof.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

What is claimed is:
 1. A method of wireless communication, comprising:establishing a first connection with a first base station, wherein thefirst connection involves the transfer of data using a first signalbased on a first segment of a frame; establishing a second connectionwith a second base station, wherein the second connection involves thetransfer of data using a second signal based on a second segment of theframe; and exchanging data with the first and second base stations viathe first and second connections within a time period bounded by theframe, wherein the first and second segments comprise different downlink(DL) data.
 2. The method of claim 1, further comprising concurrentlyprocessing the different DL data from the first and second segments. 3.The method of claim 2, wherein concurrently processing comprisesadjusting for delays between the first and second signals based on thefirst and second segments, respectively.
 4. The method of claim 3,wherein the delays comprise transmission delays between the first andsecond base stations and/or propagation delays in receiving the firstand second signals based on the first and second segments, respectively.5. The method of claim 1, further comprising: establishing a thirdconnection with a third base station, wherein the third connectioninvolves the transfer of data using a third signal based on a thirdsegment of the frame; and exchanging data with the first, second, andthird base stations via the first, second, and third connections withinthe time period bounded by the frame.
 6. The method of claim 5, whereinthe first, second, and third segments have different downlink (DL) datafrom three different services.
 7. The method of claim 1, furthercomprising: determining signal strength of the first and second signals;and deleting one of the first and second connections whose signalstrength is below a drop threshold.
 8. The method of claim 1, furthercomprising: determining signal strength of a third signal based on athird segment of a frame; and adding a third connection with a thirdbase station if the signal strength of the third signal is above an addthreshold and if the third segment uses different subchannel groups thanthe first or the second segments.
 9. The method of claim 1, furthercomprising: determining signal strength of a third signal based on athird segment of a frame; and replacing one of the first and secondconnections with a third connection to a third base station if thesignal strength of the third signal is above an add threshold and isgreater than a signal strength of the first or the second signal by atleast a margin.
 10. A receiver for wireless communication, comprising:first connection-establishing logic configured to establish a firstconnection with a first base station, wherein the first connectioninvolves the transfer of data using a first signal received by thereceiver and based on a first segment of a frame; secondconnection-establishing logic configured to establish a secondconnection with a second base station, wherein the second connectioninvolves the transfer of data using a second signal received by thereceiver and based on a second segment of the frame; and data logicconfigured to exchange data with the first and second base stations viathe first and second connections within a time period bounded by theframe, wherein the first and second segments have different downlink(DL) data and the data logic is configured to concurrently process thedifferent DL data from the first and second segments.
 11. The receiverof claim 10, wherein the data logic is configured to adjust for delaysbetween the first and second signals based on the first and secondsegments, respectively.
 12. The receiver of claim 10, further comprisingthird connection-establishing logic configured to establish a thirdconnection with a third base station, wherein the third connectioninvolves the transfer of data using a third signal based on a thirdsegment of the frame and wherein the data logic is configured toexchange data with the first, second, and third base stations via thefirst, second, and third connections within the time period bounded bythe frame.
 13. An apparatus for wireless communication, comprising:means for establishing a first connection with a first base station,wherein the first connection involves the transfer of data using a firstsignal based on a first segment of a frame; means for establishing asecond connection with a second base station, wherein the secondconnection involves the transfer of data using a second signal based ona second segment of the frame; and means for exchanging data with thefirst and second base stations via the first and second connectionswithin a time period bounded by the frame, wherein the first and secondsegments comprise different downlink (DL) data.
 14. The apparatus ofclaim 13, further comprising means for establishing a third connectionwith a third base station, wherein the third connection involves thetransfer of data using a third signal based on a third segment of theframe and wherein the means for exchanging data is a means forexchanging data with the first, second, and third base stations via thefirst, second, and third connections within the time period bounded bythe frame.
 15. A mobile device, comprising: firstconnection-establishing logic configured to establish a first connectionwith a first base station, wherein the first connection involves thetransfer of data using a first signal based on a first segment of aframe; second connection-establishing logic configured to establish asecond connection with a second base station, wherein the secondconnection involves the transfer of data using a second signal based ona second segment of the frame; and a receiver front end for receivingthe first and second signals from the first and second base stations viathe first and second connections within a time period bounded by theframe, wherein the first and second segments comprise different downlink(DL) data.
 16. The mobile device of claim 15, further comprising thirdconnection-establishing logic configured to establish a third connectionwith a third base station, wherein the third connection involves thetransfer of data using a third signal based on a third segment of theframe and wherein the receiver front end is for receiving the first,second, and third signals from the first, second, and third basestations via the first, second, and third connections within the timeperiod bounded by the frame.
 17. A non-transitory computer-readablemedium containing a program for wireless communication, which, whenexecuted by a processor, performs operations comprising: establishing afirst connection with a first base station, wherein the first connectioninvolves the transfer of data using a first signal based on a firstsegment of a frame; establishing a second connection with a second basestation, wherein the second connection involves the transfer of datausing a second signal based on a second segment of the frame; andtransferring data using the first and second connections within a timeperiod bounded by the frame, wherein the first and second segmentscomprise different downlink (DL) data.
 18. The computer-readable mediumof claim 17, further comprising concurrently processing different DLdata from the first and second segments, wherein concurrently processingcomprises adjusting for delays between the first and second signalsbased on the first and second segments, respectively.
 19. Thecomputer-readable medium of claim 17, further comprising: selectingbetween the first or the second segment based on a bandwidth grant,wherein the first and second segments are from the same service and havethe same downlink (DL) data; and using the selected segment for wirelesscommunication.
 20. A method of wireless communication, comprising:receiving signals from multiple base stations over multiple segments ofan orthogonal frequency division multiple access (OFDMA) frame;determining one or more of the segments having a best bandwidth of themultiple segments; determining another one or more of the segmentshaving another best bandwidth of the multiple segments in a differentOFDMA frame; communicating with the one or more of the segments in theOFDMA frame; and communicating with the another one or more of thesegments in the different OFDMA frame.
 21. A receiver for wirelesscommunication, comprising: first connection-establishing logicconfigured to receive signals from multiple base stations over multiplesegments of an orthogonal frequency division multiple access (OFDMA)frame; data logic configured to determine one or more of the segmentshaving a best bandwidth of the multiple segments, and determine anotherone or more of the segments having another best bandwidth of themultiple segments in a different OFDMA frame; and secondconnection-establishing logic configured to communicate with the one ormore of the segments in the OFDMA frame, and communicate with theanother one or more of the segments in the different OFDMA frame.
 22. Anapparatus for wireless communication, comprising: means for receivingsignals from multiple base stations over multiple segments of anorthogonal frequency division multiple access (OFDMA) frame; means fordetermining one or more of the segments having a best bandwidth of themultiple segments; means for determining another one or more of thesegments having another best bandwidth of the multiple segments in adifferent OFDMA frame; means for communicating with the one or more ofthe segments in the OFDMA frame; and means for communicating with theanother one or more of the segments in the different OFDMA frame.
 23. Amobile device, comprising: a receiver configured to receive signals frommultiple base stations over multiple segments of an orthogonal frequencydivision multiple access (OFDMA) frame; a processor configured todetermine one or more of the segments having a best bandwidth of themultiple segments, and determine another one or more of the segmentshaving another best bandwidth of the multiple segments in a differentOFDMA frame; and a transmitter configured to communicate with the one ormore of the segments in the OFDMA frame, and communicate with theanother one or more of the segments in the different OFDMA frame.
 24. Anon-transitory computer-readable medium containing a program forwireless communication, which, when executed by a processor, performsoperations comprising: receiving signals from multiple base stationsover multiple segments of an orthogonal frequency division multipleaccess (OFDMA) frame; determining one or more of the segments having abest bandwidth of the multiple segments; determining another one or moreof the segments having another best bandwidth of the multiple segmentsin a different OFDMA frame; communicating with the one or more of thesegments in the OFDMA frame; and communicating with the another one ormore of the segments in the different OFDMA frame.